Resin composition for golf balls, and golf ball

ABSTRACT

A resin composition for golf balls includes specific amounts of (A) polyurethane or polyurea and (B) an oxazoline group-containing acrylic polymer or an oxazoline group-containing styrene polymer. A golf ball having a core encased by a cover of one or more layers, wherein at least one cover layer is formed of this resin composition, exhibits a good adhesion between adjoining layers, enabling the ball to achieve a high scuff resistance without lowering the initial velocity of the ball.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of pending U.S. application Ser. No.16/014,058 filed Jun. 21, 2018, now allowed, which application claimspriority under 35 U.S.C. § 119(a) on Patent Application No. 2017-122257filed in Japan on Jun. 22, 2017, the entire contents of which are herebyincorporated by reference.

TECHNICAL FIELD

This invention relates to a resin composition for golf balls and to agolf ball that uses the resin composition. More particularly, theinvention relates to a golf ball in which adhesion between adjoiningcover layers is increased, providing the ball with an excellent scuffresistance without lowering its initial velocity.

BACKGROUND ART

Conventional golf balls generally have a cover structure that is formedby injection molding a material composed primarily of an ionomer resinover a core made chiefly of a diene rubber. In recent years, to improvethe feel of the ball at impact and the scuff resistance on approachshots, golf balls having a cover composed primarily of a urethanematerial such as a thermoplastic polyurethane elastomer have become morecommon.

When a urethane material is used as the cover, a good feel on impact anda high scuff resistance can be obtained. However, compared with ionomerresins, adhesion to the diene rubber serving as the chief ingredient ofthe core may be poor and, when the ball is repeatedly struck, adherenceto the core surface may worsen. Also, in golf balls having a pluralityof cover layers, the adhesive properties between urethane and ionomerresin and the adhesion with neighboring cover layers are also important.When the adhesion between layers of the golf ball is poor, this mayinvite declines in various ball properties, such as the distance, spinrate on approach shots, feel on impact, durability to cracking and scuffresistance. Hence, there exists a desire to improve the adhesion betweenlayers.

Art for improving adhesion between the layers of a golf ball has beendisclosed in a number of patent publications, one of which, JP-AH5-68724, describes the inclusion of an oxazoline group-containingthermoplastic resin in an ionomer resin-based cover material. Thispatent publication mentions that when an oxazoline group-containingthermoplastic resin is mixed into an ionomer resin under applied heat,the oxazoline groups in the thermoplastic resin react with carboxylgroups in the ionomer resin, causing the oxazoline group-containingthermoplastic resin to graft onto the surface of the ionomer resin, thusforming a compatible mixed system, or “polymer alloy,” of the oxazolinegroup-containing thermoplastic resin microdispersed within the ionomerresin. Synergistic improvements in the physical properties of thispolymer alloy enable the toughness of the ionomer resin to be furtherimproved, as a result of which the golf ball has an increaseddurability.

However, the golf ball of the foregoing art includes an oxazolinegroup-containing thermoplastic resin in a resin composition composedprimarily of an ionomer resin; it is not art relating to a resincomposition for golf balls that is composed primarily of a polyurethanematerial and used for the purpose of obtaining a high scuff resistance.

Moreover, with regard to the golf ball resin compositions made upprimarily of a urethane material such as a thermoplastic polyurethaneelastomer that have hitherto been used, there also exists a desire toachieve an even higher scuff resistance while retaining, for example, agood ball flight performance, a good spin performance and a good feel onimpact.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a golfball resin composition which can impart golf balls with a good adhesionbetween adjoining layers therein and with a high scuff resistance. Afurther object of the invention is to provide a golf ball that uses sucha resin composition.

As a result of extensive investigations, we have discovered that, in agolf ball resin composition made up primarily of polyurethane orpolyurea, by including an oxazoline group-containing acrylic polymer oran oxazoline group-containing styrene polymer as a novel compoundingingredient, the oxazoline groups in this oxazoline group-containingpolymer crosslink due to chemical bonding with, for example, urethanebonds on the polyurethane or other base polymer, thereby enabling thecrosslink density of the overall resin composition to be increased, andmoreover crosslink due to chemical bonding with carboxyl groups and thelike in the base resins of adjoining layers, thus improving adhesionbetween the layers of the golf ball and also enabling a high scuffresistance to be obtained without lowering the initial velocity of theball.

Accordingly, in one aspect, the invention provides a resin compositionfor golf balls which includes (A) polyurethane or polyurea and (B) anoxazoline group-containing acrylic polymer or an oxazolinegroup-containing styrene polymer, wherein component (B) is included inan amount of from 0.3 to 30 parts by weight per 100 parts by weight ofcomponent (A).

The acrylic polymer or styrene polymer of component (B) preferably has anumber-average molecular weight (Mn) of from 1,000 to 100,000 and aweight-average molecular weight (Mw) of from 1,000 to 250,000.

Component (B) is preferably included in an amount of from 2 to 15 partsby weight per 100 parts by weight of component (A).

In a preferred embodiment, the resin composition of the inventionfurther includes (C) a material having functional groups which reactwith oxazoline groups.

Component (C) is preferably at least one selected from the groupconsisting of polyesters, polyamides, olefin-unsaturated carboxylic acidrandom copolymers, olefin-unsaturated carboxylic acid-unsaturatedcarboxylic acid ester random copolymers, metal ion neutralizationproducts of olefin-unsaturated carboxylic acid random copolymers, andmetal ion neutralization products of olefin-unsaturated carboxylicacid-unsaturated carboxylic acid ester random copolymers.

Component (C) is preferably included in an amount of from 0.3 to 30parts by weight per 100 parts by weight of component (A).

In a second aspect, the invention provides a golf ball having a core anda cover of one or more layers which encases the core, wherein at leastone layer of the cover is formed of the resin composition according tothe first aspect of the invention.

In a preferred embodiment of the golf ball of the invention, a layeradjoining the cover layer formed of the resin composition according tothe first aspect of the invention is formed of a composition whichincludes (D) a material having functional groups which react withoxazoline groups.

In another preferred embodiment of the inventive golf ball, component(D) is at least one selected from the group consisting of polyesters,polyamides, olefin-unsaturated carboxylic acid random copolymers,olefin-unsaturated carboxylic acid-unsaturated carboxylic acid esterrandom copolymers, metal ion neutralization products ofolefin-unsaturated carboxylic acid random copolymers, metal ionneutralization products of olefin-unsaturated carboxylicacid-unsaturated carboxylic acid ester random copolymers,α,β-unsaturated carboxylic acids of 3 to 8 carbon atoms, and metal saltsof α,β-unsaturated carboxylic acids of 3 to 8 carbon atoms.

In yet another preferred embodiment of the inventive golf ball, a layeradjoining the cover layer formed of the resin composition according tothe first aspect of the invention is formed of a composition containingcomponent (D) which differs from component (C).

Advantageous Effects of the Invention

Golf balls which use the resin composition of the invention have a goodadhesion between adjoining layers, enabling a high scuff resistance tobe achieved without lowering the initial velocity of the ball.

BRIEF DESCRIPTION OF THE DIAGRAMS

FIG. 1 is a diagram showing a test specimen used for measuring theadhesion strength between cover layers (the intermediate layer and theoutermost layer) of a golf ball.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The objects, features and advantages of the invention will become moreapparent from the following detailed description taken in conjunctionwith the appended diagram.

The resin composition for golf balls according to the invention includesthe following components (A) and (B):

(A) polyurethane or polyurea, and

(B) an oxazoline group-containing acrylic polymer or an oxazolinegroup-containing styrene polymer.

The polyurethane or polyurea in component (A) is described below.

(A) Polyurethane

The polyurethane has a structure which includes soft segments composedof a polymeric polyol (polymeric glycol) that is a long-chain polyol,and hard segments composed of a chain extender and a polyisocyanate.Here, the long-chain polyol serving as a starting material may be anythat has hitherto been used in the art relating to thermoplasticpolyurethanes, and is not particularly limited. This is exemplified bypolyester polyols, polyether polyols, polycarbonate polyols, polyesterpolycarbonate polyols, polyolefin polyols, conjugated dienepolymer-based polyols, castor oil-based polyols, silicone-based polyolsand vinyl polymer-based polyols. Specific examples of polyester polyolsthat may be used include adipate-type polyols such as polyethyleneadipate glycol, polypropylene adipate glycol, polybutadiene adipateglycol and polyhexamethylene adipate glycol; and lactone-type polyolssuch as polycaprolactone polyol. Examples of polyether polyols includepoly(ethylene glycol), poly(propylene glycol), poly(tetramethyleneglycol) and poly(methyltetramethylene glycol). Such long-chain polyolsmay be used singly, or two or more may be used in combination.

It is preferable for the long-chain polyol to have a number-averagemolecular weight in the range of 1,000 to 5,000. By using a long-chainpolyol having a number-average molecular weight in this range, golfballs made with a polyurethane composition that has various excellentproperties, including resilience and productivity, can be obtained. Thenumber-average molecular weight of the long-chain polyol is morepreferably in the range of 1,500 to 4,000, and even more preferably inthe range of 1,700 to 3,500. As used herein, “number-average molecularweight” refers to the number-average molecular weight calculated basedon the hydroxyl value measured in accordance with JIS-K1557 (the sameapplies below).

The chain extender is not particularly limited; any chain extender thathas hitherto been employed in the art relating to thermoplasticpolyurethanes may be suitably used. For example, low-molecular-weightcompounds with a molecular weight of 2,000 or less which have on themolecule two or more active hydrogen atoms capable of reacting withisocyanate groups may be used. Of these, preferred use can be made ofaliphatic diols having from 2 to 12 carbon atoms. Specific examplesinclude 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol,1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. Of these, the use of1,4-butylene glycol is especially preferred.

Any polyisocyanate hitherto employed in the art relating tothermoplastic polyurethanes may be suitably used without particularlimitation as the polyisocyanate. For example, use may be made of one ormore selected from the group consisting of 4,4′-diphenylmethanediisocyanate, 2,4-toluene diisocyanate, 2,6-toluene diisocyanate,p-phenylene diisocyanate, xylylene diisocyanate, 1,5-naphthylenediisocyanate, tetramethylxylene diisocyanate, hydrogenated xylylenediisocyanate, dicyclohexylmethane diisocyanate, tetramethylenediisocyanate, hexamethylene diisocyanate, isophorone diisocyanate,norbornene diisocyanate, trimethylhexamethylene diisocyanate,1,4-bis(isocyanatomethyl)cyclohexane and dimer acid diisocyanate.

The ratio of active hydrogen atoms to isocyanate groups in the abovepolyurethane-forming reaction may be suitably selected. Specifically, inpreparing a thermoplastic polyurethane by reacting the above long-chainpolyol, polyisocyanate and chain extender, it is desirable to use therespective components in proportions such that the amount of isocyanategroups included in the polyisocyanate per mole of active hydrogen atomson the long-chain polyol and the chain extender is from 0.95 to 1.05moles.

The method for preparing the thermoplastic polyurethane is notparticularly limited. Preparation using the long-chain polyol, chainextender and polyisocyanate may be carried out by either a prepolymerprocess or a one-shot process via a known urethane-forming reaction. Ofthese, melt polymerization in the substantial absence of solvent ispreferred. Production by continuous melt polymerization using a multiplescrew extruder is especially preferred.

A commercial product may be suitably used as the polyurethane material.Illustrative examples include Pandex T7298, TR3080, T8230, T8283, T8290,T8295 and T8260 (available from DIC Covestro Polymer, Ltd.), andResamine 2593 and 2597 (available from Dainichiseika Color & ChemicalsMfg. Co., Ltd.). These may be used singly, or two or more may be used incombination.

(A) Polyurea

The polyurea is a resin composition composed primarily of urea linkagesformed by reacting (i) an isocyanate with (ii) an amine-terminatedcompound. This resin composition is described in detail below.

(i) Isocyanate

The isocyanate is preferably one that is used in the prior art relatingto thermoplastic polyurethanes, but is not particularly limited. Use maybe made of isocyanates similar to those mentioned above in connectionwith the polyurethane material.

(ii) Amine-Terminated Compound

An amine-terminated compound is a compound having an amino group at theend of the molecular chain. In this invention, the long-chain polyaminesand/or amine curing agents shown below may be used.

A long-chain polyamine is an amine compound which has on the molecule atleast two amino groups capable of reacting with isocyanate groups, andwhich has a number-average molecular weight of from 1,000 to 5,000. Inthis invention, the number-average molecular weight is more preferablyfrom 1,500 to 4,000, and even more preferably from 1,900 to 3,000.Within this average molecular weight range, an even better resilienceand productivity are obtained. Examples of such long-chain polyaminesinclude, but are not limited to, amine-terminated hydrocarbons,amine-terminated polyethers, amine-terminated polyesters,amine-terminated polycarbonates, amine-terminated polycaprolactones, andmixtures thereof. These long-chain polyamines may be used singly, or ascombinations of two or more thereof.

An amine curing agent is an amine compound which has on the molecule atleast two amino groups capable of reacting with isocyanate groups, andwhich has a number-average molecular weight of less than 1,000. In thisinvention, the number-average molecular weight is more preferably lessthan 800, and even more preferably less than 600. Such amine curingagents include, but are not limited to, ethylenediamine,hexamethylenediamine, 1-methyl-2,6-cyclohexyldiamine,tetrahydroxypropylene ethylenediamine, 2,2,4- and2,4,4-trimethyl-1,6-hexanediamine,4,4′-bis(sec-butylamino)dicyclohexylmethane,1,4-bis(sec-butylamino)cyclohexane, 1,2-bis(sec-butylamino)cyclohexane,derivatives of 4,4′-bis(sec-butylamino)dicyclohexylmethane,4,4′-dicyclohexylmethanediamine, 1,4-cyclohexane bis(methylamine),1,3-cyclohexane bis(methylamine), diethylene glycol di(aminopropyl)ether, 2-methylpentamethylenediamine, diaminocyclohexane,diethylenetriamine, triethylenetetramine, tetraethylenepentamine,propylenediamine, 1,3-diaminopropane, dimethylaminopropylamine,diethylaminopropylamine, dipropylenetriamine, imidobis(propylamine),monoethanolamine, diethanolamine, triethanolamine, monoisopropanolamine,diisopropanolamine, isophoronediamine,4,4′-methylenebis(2-chloroaniline), 3,5-dimethylthio-2,4-toluenediamine,3,5-dimethylthio-2,6-toluenediamine, 3,5-diethylthio-2,4-toluenediamine,3,5-diethylthio-2,6-toluenediamine,4,4′-bis(sec-butylamino)diphenylmethane and derivatives thereof,1,4-bis(sec-butylamino)benzene, 1,2-bis(sec-butylamino)benzene,N,N′-dialkylaminodiphenylmethane,N,N,N′,N′-tetrakis(2-hydroxypropyl)ethylenediamine, trimethylene glycoldi-p-aminobenzoate, polytetramethylene oxide di-p-aminobenzoate,4,4′-methylenebis(3-chloro-2,6-diethyleneaniline),4,4′-methylenebis(2,6-diethylaniline), m-phenylenediamine,p-phenylenediamine and mixtures thereof. These amine curing agents maybe used singly or as combinations of two or more thereof.

(iii) Polyol

Although not an essential component, in addition to the above-describedcomponents (i) and (ii), a polyol may also be included in the polyurea.In this invention, the polyol is not particularly limited, but ispreferably one that has hitherto been used in the art relating tothermoplastic polyurethanes. Specific examples include the long-chainpolyols and/or polyol curing agents mentioned below.

The long-chain polyol may be any that has hitherto been used in the artrelating to thermoplastic polyurethanes. Examples include, but are notlimited to, polyester polyols, polyether polyols, polycarbonate polyols,polyester polycarbonate polyols, polyolefin-based polyols, conjugateddiene polymer-based polyols, castor oil-based polyols, silicone-basedpolyols and vinyl polymer-based polyols. These long-chain polyols may beused singly or as combinations of two or more thereof.

The long-chain polyol has a number-average molecular weight ofpreferably from 1,000 to 5,000, and more preferably from 1,700 to 3,500.In this average molecular weight range, an even better resilience andproductivity are obtained.

The polyol curing agent is preferably one that has hitherto been used inthe art relating to thermoplastic polyurethanes, but is not subject toany particular limitation. In this invention, use may be made of alow-molecular-weight compound having on the molecule at least two activehydrogen atoms capable of reacting with isocyanate groups, and having amolecular weight of less than 1,000. Of these, the use of aliphaticdiols having from 2 to 12 carbons is preferred. Specific examplesinclude 1,4-butylene glycol, 1,2-ethylene glycol, 1,3-butanediol,1,6-hexanediol and 2,2-dimethyl-1,3-propanediol. The use of 1,4-butyleneglycol is especially preferred. The polyol curing agent has anumber-average molecular weight of preferably less than 800, and morepreferably less than 600.

A known method may be used to produce the polyurea. A prepolymerprocess, a one-shot process or some other known method may be suitablyselected for this purpose.

The proportion of the overall resin composition accounted for by thepolyurethane or polyurea serving as above component (A) is notparticularly limited, but may be set to preferably at least 60 wt %,more preferably at least 70 wt %, and even more preferably at least 80wt %.

Next, component (B) is described. Component (B) is an oxazolinegroup-containing acrylic polymer or an oxazoline group-containingstyrene polymer. The oxazoline groups on component (B) chemically bondwith urethane bonds or urea bonds on the polyurethane of component (A)that has decomposed under heat or the like, enhancing the crosslinkdensity of the resin material and making its mechanical properties morerobust. Hence, when employed in the outermost layer, component (B) canimprove the scuff resistance. In addition, it chemically bonds withcarboxyl groups and the like in the adjoining core and cover layers,enabling it to strongly adhere to the adjoining layers.

The acrylic polymer or styrene polymer of component (B) has anumber-average molecular weight (Mn) that is preferably from 1,000 to100,000, and more preferably from 10,000 to 80,000. The acrylic polymeror styrene polymer of component (B) has a weight-average molecularweight (Mw) that is preferably from 1,000 to 250,000, and morepreferably from 30,000 to 200,000. Outside of this range in themolecular weight, the compatibility with component (A) may worsen andthe durability of the ball may decline. The weight-average molecularweight (Mw) and number-average molecular weight (Mn) arepolystyrene-equivalent measured values obtained by gel permeationchromatography (GPC) using differential refractometry.

From the standpoint of achieving both the desired adhesive effect withadjoining layers and the desired durability of the invention, theoxazoline group content within the acrylic polymer or styrene polymer ofcomponent (B) is preferably from 0.1×10⁻³ to 10×10⁻³ mol/g (solids), andespecially from 0.2×10⁻³ to 8×10⁻³ mol/g (solids), per 1.0 g of thepolymer.

Having the amount of component (B) included per 100 parts by weight ofcomponent (A) be preferably from 0.3 to 30 parts by weight, morepreferably from 0.5 to 20 parts by weight, and even more preferably from2 to 15 parts by weight, is desirable for achieving both a good adhesiveeffect with adjoining layers and a good scuff resistance.

A commercial product may be used as the polymer of component (B).Illustrative examples include the acrylic polymers Epocros WS-500,Epocros WS-300 and Epocros WS-70, all of which are available from NipponShokubai Co., Ltd., and the styrene polymer Epocros RPS-1005, alsoavailable from Nippon Shokubai Co., Ltd.

Resin ingredients other than components (A) and (B) may be included. Forexample, use can be made of one or more selected from among polyesterelastomers, polyamide elastomers, ionomer resins, styrene blockelastomers, hydrogenated styrene-butadiene rubbers,styrene-ethylene/butylene-ethylene block copolymers and modified formsthereof, ethylene-ethylene/butylene-ethylene block copolymers andmodified forms thereof, styrene-ethylene/butylene-styrene blockcopolymers and modified forms thereof, ABS resins, polyacetals,polyethylenes and nylon resins. In particular, for such reasons as thefact that reaction with isocyanate groups results in increasedresilience and scuff resistance, the use of polyester elastomers,polyamide elastomers and polyacetals is especially suitable. When suchan ingredient is included, the content thereof is selected asappropriate for, e.g., adjusting the hardness, improving the resilience,improving the flow properties and improving adhesion. Although notparticularly limited, the content per 100 parts by weight of component(A) may be set to preferably at least 5 parts by weight and preferablynot more than 50 parts by weight.

In this invention, the above-described resin composition containingcomponents (A) and (B) preferably also includes: (C) a material havingfunctional groups which react with oxazoline groups. These functionalgroups in component (C) crosslink with oxazoline groups in component(B), increasing the crosslink density and thus making it possible toobtain an improved scuff resistance.

The functional groups of component (C) that react with oxazoline groupsare exemplified by carboxyl groups, thiol groups, phenolic groups andepoxy groups. In this invention, carboxyl groups are preferably used.The material of component (C) having functional groups that react withoxazoline groups is exemplified by resin materials selected from thegroup consisting of polyesters, polyamides, olefin-unsaturatedcarboxylic acid random copolymers, olefin-unsaturated carboxylicacid-unsaturated carboxylic acid ester random copolymers, metal ionneutralization products of olefin-unsaturated carboxylic acid randomcopolymers, metal ion neutralization products of olefin-unsaturatedcarboxylic acid-unsaturated carboxylic acid ester random copolymers, andphenolic resins. One, two or more of these may be used in combination.

The content of component (C), although not particularly limited, ispreferably from 0.3 to 30 parts by weight, more preferably from 2 to 20parts by weight, and even more preferably from 3 to 15 parts by weight,per 100 parts by weight of component (A). When this content is too high,the scuff resistance may decrease.

The golf ball resin composition of the invention can be obtained bymixing together the above-described components using various types ofmixers, such as a kneading-type single-screw or twin-screw extruder, aBanbury mixer, a kneader or a Labo Plastomill.

The golf ball of the invention has, over the core, a cover of one layeror a plurality of layers.

The core may be a single-layer core or a two-layer core having an innerlayer and an outer layer, or may be formed as a plurality of layers insome other arrangement.

The core can be formed using a known rubber composition. Preferredexamples include, but are not particularly limited to, the rubbercompositions formulated as shown below.

The material forming the core may be composed primarily of a rubbermaterial. For example, the core may be formed using a rubber compositionwhich includes, together with a base rubber, such ingredients as aco-crosslinking agent, an organic peroxide, an inert filler, sulfur, anantioxidant and an organosulfur compound.

The use of polybutadiene as the base rubber of the rubber composition ispreferred. It is suitable for the polybutadiene used to be one having acis-1,4 bond content on the polymer chain of preferably at least 80 wt%, more preferably at least 90 wt %, and even more preferably at least95 wt %. At a content of cis-1,4 bonds among the bonds on thepolybutadiene molecule which is too low, the resilience may decrease.The polybutadiene has a content of 1,2-vinyl bonds on the polymer chainof preferably not more than 2 wt %, more preferably not more than 1.7 wt%, and even more preferably not more than 1.5 wt %. At a 1,2-vinyl bondcontent that is too high, the resilience may decrease.

To obtain a molded and vulcanized rubber composition having a goodresilience, the polybutadiene included is preferably one synthesizedwith a rare-earth catalyst or a group VIII metal compound catalyst.Polybutadiene synthesized with a rare-earth catalyst is especiallypreferred.

Rubber components other than the above polybutadiene may be included inthe rubber composition, insofar as the objects of the invention areattainable. Illustrative examples of rubber components other than theabove polybutadiene include other polybutadienes and also other dienerubbers, such as styrene-butadiene rubber, natural rubber, isoprenerubber and ethylene-propylene-diene rubber.

Examples of co-crosslinking agents include unsaturated carboxylic acidsand the metal salts of unsaturated carboxylic acids. Specific examplesof unsaturated carboxylic acids include acrylic acid, methacrylic acid,maleic acid and fumaric acid. The use of acrylic acid or methacrylicacid is especially preferred. Metal salts of unsaturated carboxylicacids include, without particular limitation, the above unsaturatedcarboxylic acids that have been neutralized with desired metal ions.Specific examples include the zinc salts and magnesium salts ofmethacrylic acid and acrylic acid. The use of zinc acrylate isespecially preferred.

The unsaturated carboxylic acid and/or metal salt thereof is included inan amount, per 100 parts by weight of the base rubber, which may be setto preferably at least 5 parts by weight, more preferably at least 10parts by weight, and even more preferably at least 15 parts by weight.The amount included may be set to preferably not more than 60 parts byweight, more preferably not more than 50 parts by weight, and even morepreferably not more than 45 parts by weight. Too much may make the coretoo hard, giving the ball an unpleasant feel at impact, whereas toolittle may lower the rebound.

The organic peroxide may be a commercially available product, specificexamples of which include those available under the trade names PercumylD, Perhexa 3M, Perhexa C-40, Niper BW and Peroyl L (all from NOFCorporation), and Luperco 231XL (from Atochem Co.). One of these may beused alone, or two or more may be used together.

The amount of organic peroxide included per 100 parts by weight of thebase rubber is preferably at least 0.1 part by weight, more preferablyat least 0.3 part by weight, even more preferably at least 0.5 part byweight, and most preferably at least 0.7 part by weight. The upper limitis preferably not more than 5 parts by weight, more preferably not morethan 4 parts by weight, even more preferably not more than 3 parts byweight, and most preferably not more than 2 parts by weight. When toomuch or too little is included, it may not be possible to obtain a ballhaving a good feel, durability and rebound.

Examples of preferred inert fillers include zinc oxide, barium sulfateand calcium carbonate. One of these may be used alone, or two or moremay be used together.

The amount of inert filler included per 100 parts by weight of the baserubber is preferably at least 1 part by weight, and more preferably atleast 5 parts by weight. The upper limit in the amount included ispreferably not more than 100 parts by weight, more preferably not morethan 80 parts by weight, and even more preferably not more than 60 partsby weight. Too much or too little inert filler may make it impossible toobtain a proper weight and a good rebound.

In addition, an antioxidant may be optionally included. Illustrativeexamples of suitable commercial antioxidants include Nocrac NS-6, NocracNS-30 and Nocrac 200 (all available from Ouchi Shinko Chemical IndustryCo., Ltd.), and Yoshinox 425 (available from Yoshitomi PharmaceuticalIndustries, Ltd.). One of these may be used alone, or two or more may beused together.

The amount of antioxidant included can be set to more than 0, and may beset to an amount per 100 parts by weight of the base rubber which ispreferably at least 0.05 part by weight, and more preferably at least0.1 part by weight. The maximum amount included, although notparticularly limited, may be set to an amount per 100 parts by weight ofthe base rubber which is preferably not more than 3 parts by weight,more preferably not more than 2 parts by weight, even more preferablynot more than 1 part by weight, and most preferably not more than 0.5part by weight. Too much or too little antioxidant may make itimpossible to achieve a suitable core hardness gradient, a good reboundand durability, and a good spin rate-reducing effect on full shots.

An organosulfur compound may be optionally included in the rubbercomposition in order to enhance the core resilience. In cases where anorganosulfur compound is included, the content thereof per 100 parts byweight of the base rubber may be set to preferably at least 0.05 part byweight, and more preferably at least 0.1 part by weight. The upper limitin the organosulfur compound content may be set to preferably not morethan 5 parts by weight, more preferably not more than 4 parts by weight,and even more preferably not more than 2 parts by weight. Including toolittle organosulfur compound may make it impossible to obtain asufficient core rebound-increasing effect. On the other hand, when toomuch is included, the core hardness may become too low, worsening thefeel of the ball at impact, and the durability of the ball to crackingon repeated impact may worsen.

The rubber composition containing the various above ingredients isprepared by mixture using a typical mixing apparatus, such as a Banburymixer or a roll mill. When this rubber composition is used to mold thecore, molding may be carried out by compression molding or injectionmolding using a specific mold for molding cores. The resulting moldedbody is then heated and cured under temperature conditions sufficientfor the organic peroxide and co-crosslinking agent included in therubber composition to act, thereby giving a core having a specifichardness profile. The vulcanization conditions in this case are notparticularly limited, although the vulcanization is typically set tofrom about 130° C. to about 170° C.

The diameter of the core, although not particularly limited, ispreferably at least 20 mm, more preferably at least 25 mm, and even morepreferably at least 30 mm, but is preferably not more than 41 mm, andmore preferably not more than 40 mm.

The deflection of the core, expressed as the deformation when compressedunder a final load of 1,275 N (130 kgf) from an initial load of 98 N (10kgf), is preferably at least 2.0 mm, more preferably at least 2.5 mm,and even more preferably at least 2.7 mm, but is preferably not morethan 6.0 mm, and more preferably not more than 5.0 mm. When thisdeformation is too small, the feel of the ball on impact becomes toohard. On the other hand, when this deformation is too large, the feel onimpact becomes too soft or the durability of the ball to cracking underrepeated impact worsens.

It is desirable for the core to have at least a specific hardnessdifference between the center hardness and the surface hardness thereof.Setting this hardness difference, expressed in terms of JIS-C hardness,to at least 20 is preferable for obtaining the desired initial velocity,feel on impact, spin properties and durability.

The cover, which is a member that encases the core, is exemplified by asingle-layer cover and by covers consisting of a plurality of layers,such as a two-layer cover and a three-layer cover. Each layer of thecover is sometimes called a cover layer; in particular, the inner layeris called the intermediate layer and the outer layer is called theoutermost layer. In the case of a three-layer cover, the respectivelayers are called, in order from the inside: the envelope layer, theintermediate layer, and the outermost layer.

In this invention, at least one layer of the cover is formed of theabove-described golf ball resin composition containing components (A)and (B).

Moreover, in this invention, it is preferable for a layer adjoining thecover layer formed of the above-described golf ball resin compositioncontaining components (A), (B) and (C) to be formed of a compositioncontaining: (D) a material having functional groups that react withoxazoline groups. The functional groups of component (D) in thisadjoining layer, by crosslinking with oxazoline groups in the oxazolinegroup-containing polymer serving as component (B) in the above coverlayer, are able to strengthen adhesion between the layers. Component (D)is preferably a resin material that differs from component (C). Thelayer or layers adjoining the above cover layer include not only othercover layers, but also the adjoining core (when the core is composed ofa plurality of layers, the outermost core layer).

Component (D) is selected from the group consisting of polyesters,polyamides, olefin-unsaturated carboxylic acid random copolymers,olefin-unsaturated carboxylic acid-unsaturated carboxylic acid esterrandom copolymers, metal ion neutralization products ofolefin-unsaturated carboxylic acid random copolymers, metal ionneutralization products of olefin-unsaturated carboxylicacid-unsaturated carboxylic acid ester random copolymers, phenolicresins, and rubber compositions. One or more of these may be used. Whenusing a rubber composition, it is preferable to employ a rubbercomposition containing an α,β-unsaturated carboxylic acid of 3 to 8carbon atoms and/or a metal salt thereof. The α,β-unsaturated carboxylicacid of 3 to 8 carbon atoms and/or a metal salt thereof is mostpreferably zinc acrylate.

For example, when the layer adjoining the cover layer is formed of, ascomponent (D), an acid (carboxyl group)-containing polymer such as anionomer resin, these carboxyl groups, by crosslinking with oxazolinegroups in component (B) included in the above cover layer, are able toincrease adhesion between the cover layer and the adjoining layer.

Various additives may be optionally included in the materials that formthe respective cover layers. For example, pigments, dispersants,antioxidants, light stabilizers, ultraviolet absorbers and internal moldlubricants may be suitably included.

The thicknesses of the respective layers, although not particularlylimited, are preferably at least 0.5 mm, and more preferably at least0.7 mm, but are preferably not more than 1.2 mm, more preferably notmore than 1.1 mm, and even more preferably not more than 0.9 mm.

The hardnesses of the respective layers on the Shore D scale, althoughnot particularly limited, are set to preferably at least 30, and morepreferably at least 40, but preferably not more than 75, more preferablynot more than 70, and even more preferably not more than 65.

A known method may be used without particular limitation as the methodof forming the layers of the cover. For example, use can be made of amethod in which a pre-fabricated core or a sphere composed of the coreencased by any of various layers is placed in a mold, and the resinmaterial prepared as described above is injection-molded over the coreor layer-encased sphere.

The ball has a deflection, measured as the deformation when the sphereis compressed under a final load of 1,275 N (130 kgf) from an initialload of 98 N (10 kgf), which is preferably at least 2.0 mm, and morepreferably at least 2.5 mm, but is preferably not more than 4.0 mm, andmore preferably not more than 3.8 mm. When the deformation is too small,the feel of the ball on impact may be too hard. On the other hand, whenthe deformation is too large, the feel on impact may be too soft or thedurability to cracking on repeated impact may worsen.

Numerous dimples of one, two or more types may be formed on the surfaceof the cover. In addition, various types of coatings may be applied tothe cover surface. Given the need for the golf ball to withstand harshconditions of use, preferred examples of such coatings include two-partcuring urethane coatings, especially non-yellowing urethane coatings.

Ball specifications such as the ball mass (weight) and diameter may beset as appropriate according to the Rules of Golf.

EXAMPLES

The following Working Examples and Comparative Examples are provided toillustrate the invention, and are not intended to limit the scopethereof.

Working Examples 1 to 12, Comparative Examples 1 to 5

Using the following rubber composition shown in Table 1 below, which wascommon to all the examples, solid cores for the respective examples wereproduced by 15 minutes of vulcanization at 155° C.

TABLE 1 Rubber composition for core (C1) Parts by weightcis-1,4-Polybutadiene 100 Zinc acrylate 27 Zinc oxide 4.0 Barium sulfate16.5 Antioxidant 0.2 Organic Peroxide (1) 0.6 Organic Peroxide (2) 1.2Zinc salt of pentachlorothiophenol 0.3 Zinc stearate 1.0

Details on the above core materials are given below.

-   cis-1,4-Polybutadiene: Available under the trade name “BR01” from    JSR Corporation-   Zinc acrylate: Available from Nippon Shokubai Co., Ltd.-   Zinc oxide: Available from Sakai Chemical Co., Ltd.-   Barium sulfate: Available from Sakai Chemical Co., Ltd.-   Antioxidant: Available under the trade name “Nocrac NS-6” from Ouchi    Shinko Chemical Industry Co., Ltd.-   Organic Peroxide (1): Dicumyl peroxide, available under the trade    name “Percumyl D” from NOF Corporation-   Organic Peroxide (2): A mixture of    1,1-di(tert-butylperoxy)cyclohexane and silica, available under the    trade name “Perhexa C-40” from NOF Corporation-   Zinc stearate: Available from NOF Corporation    Formation of Cover Layers (Intermediate Layer and Outermost Layer)

Next, intermediate layer-encased spheres were produced by using theresin materials formulated as shown in Tables 2 and 3 below to injectionmold a 1.3 mm thick intermediate layer over the 38.5 mm diameter coresobtained above. In each example, an outermost layer having a thicknessof 0.8 mm was then injection molded over the intermediate layer-encasedsphere using the appropriate resin material formulation in Table 2 or 3,thereby producing a three-piece golf ball. A common arrangement ofdimples was formed at this time on the surface of the cover in eachWorking Example and Comparative Example.

TABLE 2 Cover composition (pbw) M-1 M-2 M-3 M-4 M-5 M-6 M-7 M-8 M-9 M-10(A) Polyurethane 100 100 100 100 100 100 100 100 100 (B)Oxazoline-containing polymer 0.5 0.5 0.5 3 3 3 3 10 10 (C) Polyesterelastomer 3 12 3 12 3 12 (C) Acid copolymer 12 (D) 100

TABLE 3 Cover composition (pbw) M-11 M-12 M-13 M-14 M-15 M-16 N-1 (A)Polyurethane 100 100 100 100 100 100 (B) Oxazoline- 0.2 0.2 3 containingpolymer (C) Polyester 3 3 25 12 elastomer (D) Na-based 50 ionomerZn-based 50 ionomer

Details on the ingredients mentioned in the tables are given below.

-   (B) Oxazoline-containing polymer: The styrene polymer Epocros    RPS1005 (oxazoline group content, 0.27 mmol/g of solids; glass    transition temperature, 109° C.; number-average molecular weight    (Mn), 70,000; weight-average molecular weight (Mw), 160,000),    available from Nippon Shokubai Co., Ltd.-   (C) Polyester elastomer: Hytrel 4001, from DuPont-Toray Co., Ltd.-   (C), (D) Acid copolymer: An ethylene-unsaturated carboxylic acid    copolymer having an acid content of 8 wt %-   (D) Na-Based ionomer: The sodium neutralization product of an    ethylene-unsaturated carboxylic acid copolymer having an acid    content of 18 wt %-   (D) Zn-Based ionomer: The zinc neutralization product of an    ethylene-unsaturated carboxylic acid copolymer having an acid    content of 15 wt %-   (A) Polyurethane: A resin material formulated as shown in Table 4    below.

TABLE 4 Polyurethane resin formulation Parts by weight T-8290 75 T-828325 Titanium oxide 3.5 Isocyanate compound 7.5

Trade names for the chief materials in Table 4 are given below.

-   T-8290, T-8283: Ether-type thermoplastic polyurethanes available    under the trade name Pandex from DIC Covestro Polymer, Ltd.-   Isocyanate compound: 4,4′-Diphenylmethane diisocyanate

Various properties of the resulting golf balls, including the diametersand deformation under specific loading (deflection) of the core,intermediate layer-encased sphere and ball, were evaluated by themethods described below. The results are shown in Tables 5 and 6. Inaddition, the initial velocity, adhesion and scuff resistance of thegolf balls produced in the respective examples were evaluated by thefollowing methods. Those results are likewise presented in Tables 5 and6.

Diameter of Core and Intermediate Layer-Encased Sphere

The diameters at five random places on the surface were measured at atemperature of 23.9±1° C. and, using the average of these measurementsas the measured value for a single core or intermediate layer-encasedsphere, the average diameter for five measured specimens was determined.

Ball Diameter

The diameters at five random dimple-free areas on the surface weremeasured at a temperature of 23.9±1° C. and, using the average of thesemeasurements as the measured value for a single ball, the averagediameter for five measured balls was determined.

Ball Deflection

The ball was placed on a hard plate and the amount of deflection whencompressed under a final load of 1,275 N (130 kgf) from an initial loadof 98 N (10 kgf) was measured. The amount of deflection here refers tothe measured value obtained after holding the specimen isothermally at23.9° C.

Initial Velocity of Ball

The initial velocity was measured using an initial velocity measuringapparatus of the same type as the USGA drum rotation-type initialvelocity instrument approved by the R&A. The ball wastemperature-conditioned for at least 3 hours at a temperature of 23±1°C., and then tested in a chamber at a room temperature of 23±2° C. Tenballs were each hit twice, the time taken for the ball to traverse adistance of 6.28 g (1.91 m) was measured, and the initial velocity wascalculated. The initial velocity results shown in Tables 5 and 6 arevalues relative to an arbitrary index of 100 for the initial velocitymeasured in Comparative Example 1.

Adhesion Strength

Referring to FIG. 1, letting p1 be a plane at a distance of 2 mm fromthe center of a golf ball 10 and p2 be a plane having point symmetrywith p1 through the ball center, the adhesion strength between theoutermost layer 30 and the intermediate layer 20 was measured in theball region s1 between the two planes p1 and p2. First, cuts T were madein the outermost layer 30 of the ball where p1 and p2 respectivelyintersect the outermost layer 30, and those portions of the outermostlayer 30 other than s1 were peeled off. Next, a cut T perpendicular top1 and p2 was made in the outermost layer 30 and, starting at this cut,about 20 mm of the outermost layer 30 was peeled from the intermediatelayer 20, thereby obtaining a test specimen having a partially peeledstrip thereon for gripping. The test was then carried out by grippingthe strip provided in the outermost layer 30 with the movable clamp of atensile tester. A test specimen-immobilizing fixture allows the testspecimen to rotate while maintaining its center position, enabling theoutermost layer 30 wrapped around the intermediate layer 20 to be peeledoff without slack as the clamp moves away. Based on JIS K6256 (“AdhesionTest Method for Vulcanized Rubber and Thermoplastic Rubber”), themovable clamp of the tensile tester was moved at a speed of 50 mm/minand the tensile strength was measured at 0.1 mm intervals. The tensilestrengths over an approximately 100 mm length of the outermost layer 30were measured for each of three test specimens, and the average of themeasured values for the three specimens was treated as the adhesionstrength (units: N). The adhesion strength results shown in Tables 5 and6 are values relative to an arbitrary index of 100 for the adhesionstrength between the outermost layer and the intermediate layer inComparative Example 1.

When measuring the adhesive strength between the core and theintermediate layer, the intermediate layer was peeled off with, in FIG.1, the symbol 30 representing the intermediate layer and the symbol 20representing the core, and measurement was similarly carried out. Theadhesion strength results shown in Tables 5 and 6 are values relative toan arbitrary index of 100 for the adhesion strength between theintermediate layer and the core in Comparative Example 5.

Scuff Resistance

The golf balls were held isothermally at 23° C. and five balls of eachtype were hit at a head speed of 33 m/s using as the club a pitchingwedge mounted on a swing robot machine. The damage to the ball from theimpact was visually rated based on the following 5-point scale.

5: No damage or substantially no apparent damage.

4: Damage is apparent but so slight as to be of substantially noconcern.

3: Surface is slightly frayed.

2: Some fraying of surface or loss of dimples.

1: Dimples completely obliterated in places.

The average score was calculated for each type of ball. The scuffresistances shown in Tables 5 and 6 are values relative to an arbitraryindex of 100 for the average score obtained in Comparative Example 1.

TABLE 5 Working Example 1 2 3 4 5 6 7 8 9 Construction 3-piece 3-piece3-piece 3-piece 3-piece 3-piece 3-piece 3-piece 3-piece Layer in whichresin composition outermost outermost outermost outermost outermostoutermost outermost outermost intermediate of invention is used layerlayer layer layer layer layer layer layer layer Core Composition C1 C1C1 C1 C1 C1 C1 C1 C1 Diameter (mm) 38.5 38.5 38.5 38.5 38.5 38.5 38.538.5 38.5 Weight (g) 34.5 34.5 34.5 34.5 34.5 34.5 34.5 34.5 34.5Intermediate Composition N-1 N-1 N-1 N-1 N-1 N-1 N-1 M-10 M-6 layerIntermediate Diameter (mm) 41.1 41.1 41.1 41.1 41.1 41.1 41.1 41.1 41.1layer-encased Weight (g) 40.6 40.6 40.6 40.6 40.6 40.6 40.6 40.6 40.6sphere Outermost Composition M-1 M-2 M-3 M-4 M-5 M-6 M-7 M-6 N-1 layerBall Diameter (mm) 42.7 42.7 42.7 42.7 42.7 42.7 42.7 42.7 42.7 Weight(g) 45.4 45.4 45.4 45.4 45.4 45.4 45.4 45.4 45.4 Deflection (mm) 2.7 2.72.7 2.7 2.7 2.7 2.7 2.7 2.7 Initial velocity 100 100 100 100 100 100 100100 100 (index) Adhesion Outermost layer/ 200 220 180 200 220 250 250250 250 Intermediate layer (index) Intermediate layer/ — — — — — — — —180 Core (index) Scuff resistance (index) 200 200 180 200 250 250 250250 100

TABLE 6 Working Example Comparative Example 10 11 12 1 2 3 4 5Construction 3-piece 3-piece 3-piece 3-piece 3-piece 3-piece 3-piece3-piece Layer in which resin composition outermost outermost outermostoutermost outermost outermost outermost intermediate of invention isused layer layer layer layer layer layer layer layer Core Composition C1C1 C1 C1 C1 C1 C1 C1 Diameter (mm) 38.5 38.5 38.5 38.5 38.5 38.5 38.538.5 Weight (g) 34.5 34.5 34.5 34.5 34.5 34.5 34.5 34.5 IntermediateComposition N-1 N-1 N-1 N-1 N-1 N-1 N-1 M-16 layer Intermediate Diameter(mm) 41.1 41.1 41.1 41.1 41.1 41.1 41.1 41.1 layer-encased Weight (g)40.6 40.6 40.6 40.6 40.6 40.6 40.6 40.6 sphere Outermost Composition M-8M-9 M-15 M-11 M-12 M-13 M-14 N-1 layer Ball Diameter (mm) 42.7 42.7 42.742.7 42.7 42.7 42.7 42.7 Weight (g) 45.4 45.4 45.4 45.4 45.4 45.4 45.445.4 Deflection (mm) 2.7 2.7 2.7 2.7 2.7 2.7 2.7 2.7 Initial velocity100 100 100 100 100 100 100 100 (index) Adhesion Outermost layer/ 250250 230 100 100 110 110 100 Intermediate layer (index) Intermediatelayer/ — — — — — — — 100 Core (index) Scuff resistance (index) 250 250190 100 100 110 120 100

The results in Tables 5 and 6 demonstrate that the golf balls obtainedin Working Examples 1 to 12 all had good scuff resistances and,moreover, adhesion with the adjoining layer (intermediate layer or core)was satisfactory. By contrast, because the golf balls obtained in bothComparative Examples 1 and 2 contained no component (B), the scuffresistance was not good and adhesion with the intermediate layer wasinadequate. In both Comparative Examples 3 and 4, because the content ofcomponent (B) was low, the scuff resistance was poor and adhesion withthe intermediate layer was inadequate. Comparative Example 5 is anexample in which component (B) was not included in the intermediatelayer material. As a result, adhesion with, as the adjoining layers, theoutermost layer and the core was found to be inadequate.

Japanese Patent Application No. 2017-122257 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

The invention claimed is:
 1. A golf ball comprising a core and a coverof one or more layers which encases the core, wherein at least one layerof the cover is formed of the resin composition, comprising: (A)polyurethane or polyurea, (B) an oxazoline group-containing acrylicpolymer or an oxazoline group-containing styrene polymer, and (C) amaterial having functional groups which react with oxazoline groups,wherein component (B) is included in an amount of from 0.3 to 30 partsby weight per 100 parts by weight of component (A) and wherein component(C) is polyesters or polyamides, and the proportion of the polyurethaneor polyurea serving as component (A) in the overall resin compositionaccounted for at least 60 wt %.
 2. The golf ball of claim 1, wherein alayer adjoining the cover layer formed of the resin composition of claim1 is formed of a composition comprising (D) a material having functionalgroups which react with oxazoline groups.
 3. The golf ball of claim 2,wherein component (D) is at least one selected from the group consistingof polyesters, polyamides, olefin-unsaturated carboxylic acid randomcopolymers, olefin-unsaturated carboxylic acid-unsaturated carboxylicacid ester random copolymers, metal ion neutralization products ofolefin-unsaturated carboxylic acid random copolymers, metal ionneutralization products of olefin-unsaturated carboxylic acidunsaturated carboxylic acid ester random copolymers, α,β-unsaturatedcarboxylic acids of 3 to 8 carbon atoms, and metal salts ofα,β-unsaturated carboxylic acids of 3 to 8 carbon atoms.
 4. The golfball of claim 3, wherein the selected kind of component (D) differs fromthe material of component (C).
 5. The golf ball of claim 1, wherein theacrylic polymer or styrene polymer of component (B) has a number-averagemolecular weight (Mn) of from 1,000 to 100,000 and a weight-averagemolecular weight (Mw) of from 1,000 to 250,000.
 6. The golf ball ofclaim 1, wherein component (B) is included in an amount of from 2 to 15parts by weight per 100 parts by weight of component (A).
 7. The golfball of claim 1, wherein component (C) is included in an amount of from0.3 to 30 parts by weight per 100 parts by weight of component (A). 8.The golf ball of claim 1, wherein the oxazoline group content within theacrylic polymer or styrene polymer of component (B) is from 0.1×10⁻³ to10×10⁻³ mol/g (solids).
 9. The golf ball of claim 1, wherein all of theresin components consists of component (A), component (B) and component(C).